1. Field of the Invention
The present invention relates to a plasma matrix display unit for presenting alphanumeric data and graphics.
2. Description of the Prior Art
More particularly, this invention concerns a plasma display unit or panel having an operation analogous to that of the writing head for a facsimile reproduction apparatus disclosed in U.S. Pat. No. 4,021,851. According to this Patent, the writing head for printing aligned points on a light sensitive surface is essentially formed by a tight enclosure which contains a low pressure rare gas. The enclosure is constituted by rear and front parallel rectangular insulating plates which are joined by a leak-tight seal at the periphery of the enclosure. The front plate is transparent. A first and second parallel metallic strips constitute the scan anode and the display anode and extends longitudinally on the internal surface of the front insulating plate. Third parallel metallic strips constitute the scan cathodes and the trigger cathode and extends orthogonally to and at a predetermined distance from the anodes on the rear insulating plate. The gastight enclosure also includes an insulating spacer which maintains the internal surface of both plate at the predetermined distance and which has a longitudinal slot therein. The width of the longitudinal slot is substantially equal to the entire width of the two anodes and contains these anodes. In fact, the slot constitutes the gastight enclosure. The display anode is perfored longitudinally of a plurality of equidistant aligned holes in front of which pass the scan cathodes.
According to the U.S. Pat. No. 4,021,851, the rear plate is generally of forsterite (natural silicate of magnesium) so that the insulating elements such as the insulating spacer are of an insulating compound suitable for high temperature serigraphy. During manufacture of a display unit of this type, the various heating operations deform the electrodes as a result of the contractions of the materials used. Consequently a display unit construction of this type cannot be used for a display matrix unit of large dimensions, as the deformations cause a variation of the predetermined distance along one anode. This does not enable PASCHEN minimum to be obtained with a great accurate between one anode and one cathode at the level of each point of the front plate, this being necessary for the desired localisation and accurate dimensions of a luminous spot which is obtained on the surface of a cathode by discharge of inert gas into the enclosure.
It is to be noted that this type of plasma display unit in which the control of the electrodes is a direct current and the display cells are each defined by the intersection of at least one display anode and a cathode, is described in a general manner in paragraph 4 of the article of G. F. Weston, in Journal of Physics E, scientific instruments, vol. 8, No. 12, December 1975, London. A particular display unit of this type, in which each cathode of a cell is in series with a load resistance printed on the second plate is also disclosed in the U.S. Pat. No. 3,718,483.
All the plasma display units according to this prior art have at least the second conducting strips, i.e. display anodes which are supported on the first plate, i.e. the upper front transparent plate, and the third conducting strips, i.e. cathodes which are supported on the second plate, i.e. the lower rear plate. They therefore have the above-mentioned drawbacks.